Roof and waterproofing membranes and linings have long been used to protect buildings, to contain water in ponds and decorative water features, to prevent leaching of contaminants from landfills, and for other purposes. While these membranes have utility, leakage through the membranes is an ongoing problem. The efforts to contain and locate leakage have resulted in the rise of specialized consultants, air and vacuum testable membranes, and electrical testing methods that not only determine if a leak is present in a membrane system, but where the leak is located.
Leakage in existing roofs is a particular problem, especially when the roof has a nonconductive element at the bottom of the roofing envelope next to the deck, such as a vapor barrier or a secondary roofing membrane. In these cases, water leaking into the roofing envelope can saturate the insulation and other elements in the envelope without actually leaking into the building because the lowermost membrane acts as a barrier to the water. In time, water might run into the building via penetrations, such as vent stacks, curbs for mechanical equipment, conduits, etc., through the roofing envelope and be visible from underneath. By this time, corrective action may be as extensive as cutting cores in the roofing envelope to determine the extent of water damage, removing a large portion of the roof; performing infrared or other tests to indicate the current status of the roofing envelope; etc.
Additionally, when the roofing envelope becomes saturated with water, a portion of the planned energy efficiency from the roofing envelope is lost. The building structure may also experience the corrosive effects of water, therefore compromising its penetrations. Unbeknownst to anyone, this process is occurring in thousands of roofs across North America and, indeed, in the built environment anywhere in the world.
There are methods that have been developed to address the above described problems including manual methods, such as capacitance testing, infrared scanning, and moisture probing. In addition, there are automatic systems driven by computers with sensors built into or retrofitted into the non-conductive insulation and other non-conductive materials which comprise the roofing envelope.
One known method of placing such an automatic system into a non-conductive envelope is to install relative humidity sensors in the roofing envelope, where the sensors measure humidity and temperature. An array of such sensors can give a representation of moisture conditions in a roofing envelope. Such a system is provided by Progeo GmbH of Germany and other vendors, and these systems have been used on projects in the United States. Such systems are limited in that the sensors require a certain amount of free air around them in order to determine the ambient moisture content of any part of the roofing envelope, and each sensor is only one point, measuring the relative humidity of a very small area around its location. Further, there is no guarantee that any air will circulate in the roofing envelope, and if the free flow of air is cut off, especially given the impermeable nature of closed-cell insulations in today's roofing envelopes, the sensors will not be able to sense variations in moisture, but only temperature changes.
In addition, the Inventor has developed several automatic systems, such as those disclosed in U.S. Pat. Nos. 8,566,051 and 9,341,540 and co-pending U.S. patent application Ser. Nos. 13/442,586, 14/061,480, and 14/107,694, and U.S. Provisional Application No. 62/237,948, each of which is hereby incorporated by reference.
Another known automatic system requires a grid of hydrophobic cables, the cross-over points of which, when wetted from water flowing through the roofing membrane, make a closed circuit that identifies which portion of the grid is wet and allows location of the leakage through the membrane. This system requires water to make its way to the cross-over points to trigger an alarm and a significant flooding of a portion of the roofing envelope might occur before an alarm is tripped. Such a system is sold under the trademark DETEC.
Most electronic leak detection systems for roofing and waterproofing utilize the ability of the roofing or waterproofing membrane to resist the passage of electrical current through the membrane. In theory, this property electrically isolates the sensors positioned on one side of the membrane from the voltage produced by the same leak detection system on the other side of the membrane. When the membrane is breached and water flows from one side to the other, the circuit between the side with the voltage and the side with the sensors is closed, allowing the sensor to detect the voltage, thus theoretically allowing the leak detection processor connected to the sensors to determine that a leak has occurred and where that leak is coming from. Again in theory, electrically non-conductive membranes would show no voltage on the sensor side of the membrane until a breach occurred, at which time the voltage detected would be sufficiently large that the system could determine that there was an actual leak occurring and where that leak was located based on triangulation of voltage values from the various sensors.
However, it has become apparent through use of existing leak detection systems, as referenced above, that a significant number of roofing and waterproofing membranes can develop degrees of electrically conductive properties, or already have electrically conductive properties, and that these membranes allow a considerable amount of current to pass through the membrane itself without the membrane being breached. While some membranes are intrinsically conductive, and this is a known property of those membranes, others become conductive over time when immersed in water or soils and chemicals used in planting, such as fertilizers, pesticides that the like. This conductivity can, and often does, interfere with electronic leak detection, providing false positive readings or confounding the system when a leak actually does occur because the membrane is already allowing current to pass through, narrowing the window of what level of voltage would indicate a leak and what level would not indicate a leak. Further, the membranes do not become uniformly conductive, so voltage readings on the side of the membrane to which the sensors are applied can vary greatly, further exacerbating the problem of determining leakage.
Through empirical study of membranes already installed with leak detection in real-world projects, we now know that, if a membrane becomes conductive over time, a small point of contact with an electrode will begin to show a small amount of voltage on the other side of the membrane, while an electrode that has a greater area of contact will produce a larger amount of voltage through the membrane. Further, it is apparent that a conductive mesh or other medium covering the entire surface under the membrane, if energized, can act as one big, overall electrode, and can provide enough voltage through the membrane that readings by the sensors or electrodes on the other side of the membrane become so large that an actual leak, which one would expect to result in a spike in the voltage readings at any electrode near the leak, are nearly undetectable.
U.S. Pat. No. 8,566,051 discloses sensors or electrodes that can be applied to the top surface of the membrane and are used to determine if a grounding condition that would indicate a leak exists. This patent also refers to a conductive loop that forms a “pool” of electrical tension on the top surface of the membrane, and a mesh or conductive medium below the membrane that is grounded to the structure or earth so that the current can flow through a breach in the membrane to ground, and the voltage measured on the surface by the electrodes decreases as the distance to the breach decreases.
Prior art also discloses that the mesh or conductive medium under the membrane, if not grounded to the structure, can be energized and voltages can be read manually or by what is known as the two-pole method as disclosed in U.S. Pat. No. 4,565,965 to Geesen, for example. It has been found, however, that a conductive membrane can confound these manual methods. Again, this is because the detected voltages have higher readings, thus narrowing the window of discovery for the even higher voltages that emanate from a breach in the membrane. In addition, detected voltages can also become irregular from point to point because conductivity of the membrane can vary considerably.
It is therefore advantageous to develop a method that can measure actual leakage and breaches in any part of the membrane with as little interference as possible from the current that is already flowing through the membrane. Current may be already flowing through the membrane, if, for example, the membrane is conductive or becomes conductive when in service, or has areas of differing conductivity.